1. Field of the Invention
The present invention relates to a method of forming an organic film, and to an organic film, a nozzle plate, an inkjet head and an electronic device, and more particularly to technology for forming an organic film using a silane coupling agent.
2. Description of the Related Art
An organic film using a silane coupling agent can be formed on various base members, and therefore is applied in a wide range of fields. In the field of inkjet technology, a film of this kind is used when forming a liquid-repellent film on the ejection surface of a nozzle plate, or when bonding two base members together, or the like, and beneficial effects are achieved in improving the ejection characteristics, the maintenance properties and the durability of the head.
For example, Japanese Patent Application Publication No. 2001-105597 discloses an liquid ejection head used in an ink-jet recording apparatus, in which, in order to prevent damage of the ejection surface of a nozzle plate and degradation of a blade and maintain orifices in an excellent state preventing adherence of contamination to the ejection surface for a long time, the ejection surface is coated with a material having an ultrahigh water-repellent property, and heat treatment at 150° C. is performed after the coating process.
However, during the course of the reaction to form an organic film with a silane coupling agent, there have been situations where island-shaped projections are formed on the surface of the organic film. The island-shape projections are thought to be formed due to the layering, over the film, of the unreacted silane coupling agent or the polymerized silane coupling agent that is not bonded to the base member. It is difficult to remove these island-shaped projections in the processing (e.g., baking process) after formation of the film, and hence in order to suppress the projections, it has been necessary to control the film formation conditions very strictly at the film formation stage.
In particular, there has been a problem in that if island-shaped projections are formed in the vicinity of nozzles in the liquid-repellent film used on a nozzle plate of an inkjet head, then the ejection performance declines. Moreover, the island-shaped projections become detached during maintenance using a blade, or the like, and these detached projections can move inside the nozzles and block the nozzles, thus reducing the ejection accuracy.
Possible methods of removing the island-shaped projections are a method involving mechanical removal using a blade or the like, and a method involving immersion in a fluoric solvent. However, a mechanical removal method may cause damage to the nozzle surface and the liquid-repellent film itself, in addition to leading to the above-described movement of removed material inside the nozzles. Moreover, if removal is performed using a fluoric solvent, then although the projections can be removed easily if the process is carried out immediately after film formation, the film thickness is greatly reduced compared to the initial film thickness, and hence the durability of the film is markedly reduced. For example, when a silane coupling type liquid-repellent film was deposited on a silicon substrate and then immersed in a fluoric solvent (Asacrin AE-3000 manufactured by Asahi Glass) for 1 minute, then although the surface of the organic film was made smooth, the film thickness was reduced to about 10 nm or less from an initial thickness of 25 nm. Furthermore, when the alkali resistance of samples was checked in relation to the inclusion or omission of the fluoric solvent processing, a sample processed with the fluoric solvent had less than one half of the resistance of an unprocessed sample.